Jon K., I've done exactly this with an ETC IRA and and ETC 401k. I can probably help you with the wording on the partnership docs, but the problem is this. When you submit your DOI to ETC, they will review it and if they don't like something about it, will refuse to fund and will require changes.
So "Time is of the esssence" and "Equity Trust" are not two concepts that work together well. This is exactly the reason that I placed my new inherited IRA with Udirect, based on @Bryan Hancock's recommendation. They have been awesome to deal with in comparison, and I am very happy with them. I still have investors in my lending business who use ETC, and I dread each transaction. In fact, I'm in a dispute with them right now about a Roth 401k contribution. They are horrible to work with.
So, if you PM or email me separately, I can probably help with the wording for the JV agreement, and then you can take it from there. I'm up early so will answer you then.